The comparison of the rate of onset, duration of action, relative efficacy and pharmacokinetics of a single dose of intravenous omeprazole with a single dose of oral omeprazole in patients with Zollinger Ellison Syndrome was studied. 9 patients have been studied with pharmacokinetics estimates and gastric acid output data collected. Results indicate a wide variability on the bioavailability, clearance, and volume of distribution between patients, although the half-life was similar. Gastric acid output was completely inhibited upon administration of omeprazole and remained so while detectable levels of the drug was present. Further studies in this patient population will continue.